The present invention relates to implantable medical devices, and more particularly to an implantable microminiature stimulator (or "microstimulator") or microminiature sensor (or "microsensor") adapted to securely attach to one or more muscle or nerve fibers (or muscles or nerves) and to electrically stimulate the muscle nerve at the point of attachment in a controlled manner, or to sense one or more specific parameters that originate at or near the point of attachment. More particularly, the invention relates to an implantable microstimulator and/or microsensor (hereafter referred to as a "microdevice" or "microdevices") that uses helical electrodes for sensing, stimulating, and/or anchoring.
Neurological disorders are often caused by neural impulses failing to reach their natural destination in otherwise functional body systems. Local nerves and muscles may function, but, for various reasons, injury, stroke, or other cause, the stimulating nerve signals do not reach their natural destination. For example, paraplegics and quadriplegics have intact nerves and muscles and only lack the brain to nerve link, which stimulates the muscles into action.
Prosthetic devices have been used for some time to provide electrical stimulation to excite muscles, nerves or other tissues. Such devices have ranged in size and complexity from large, bulky systems feeding electrical pulses by conductors passing through the skin, to small, implanted stimulators which are controlled through telemetry signals, such as are discussed in U.S. Pat. No. 4,524,774 (invented by Hildebrandt). Other devices have comprised a centrally-implanted stimulator package sending stimulation signals to a multitude of distant target sites using a network of implantable leads and electrodes. Unfortunately, when a lead and electrode are attached to a muscle or nerve from a centrally-implanted stimulator package, the muscle or nerve is, in effect, tethered by the lead, which may cause discomfort, irritation and damage to the patient as the muscle or nerve moves with a limb or body organ associated with the muscle or nerve. What is needed, therefore, is a way to stimulate a muscle or nerve without tethering the muscle or nerve.
Complications, including the possibility of infection, arise in the use of muscle, nerve or other stimulators which have conductors extending through the skin or which have nerve-stimulating electrodes that puncture or penetrate the epineurium. Further, in the use of implanted stimulators, difficulties arise in providing suitable, operable stimulators which are small in size and have the capability to receive and store sufficient energy and control information to satisfactorily operate them without direct connection. Hence, what is needed is an implantable stimulator that avoids the use of through-the-skin conductors, epineurium-penetrating electrodes, or other tissue-penetrating electrodes, and is small enough to facilitate easy implantation, yet has sufficient capacity to receive and store energy and control information so as to provide useful muscle or nerve stimulation.
Disadvantageously, the construction of a tiny microstimulator or microsensor (microdevice) presents problems of its own, which are not encountered in the construction of larger-sized biomedical appliances. An extremely small size involves problems and solutions of a different nature than are ordinarily encountered. The appropriate design of a suitable, small microdevice which can be easily implanted, such as by expulsion through the lumen of a needle, is difficult to achieve. Notwithstanding the small size and required shape, the microdevice structure must contain means for receiving and storing sufficient energy to provide the desired stimulating pulses or the desired sensing function, as well as electronic circuitry that provides control of the characteristics desired for the stimulating pulse or sensing signal.
Further, the electrodes used with a microdevice must also be carefully selected. Such electrodes must not complicate the implantation process, i.e., the electrodes too must be small and flexible, yet be of sufficient strength and length to be securely attached to the muscle or nerve they are to stimulate or from (or near) which a desired parameter is to be sensed.
The present invention advantageously addresses the above and other needs.